THE FOSSIL RECORD 23 



tions. In the South of England the Tertiaries 

 are very well developed the London basin, 

 for example, is occupied by strata of this age, 

 the Bagshot Sands, the London Clay, and the 

 Woolwich and Reading beds. In the Isle of 

 Wight and on the Hampshire coast, Tertiary 

 deposits of later date are well shown. 



In the Cretaceous formation we reach the 

 great Secondary or Mesozoic period. The geo- 

 logical boundaries, however, do not correspond 

 here to any important change in the vegetation. 

 Many of the modern types extend through the 

 Upper, and some down to the Lower Cretaceous. 

 In the latter, however, we find a more antique 

 Flora, with Gymnosperms (Conifers and their 

 allies) as the dominant class; the Chalk, so 

 characteristic of South-eastern England, may 

 serve to represent the Upper Cretaceous, while 

 the Lower Greensand, well developed hi Kent, 

 Surrey and Sussex, is a good example of the 

 Lower Cretaceous strata. At the base of the 

 Cretaceous is an important formation the Weal- 

 den so named from the Weald of the three 

 counties just mentioned. It is a fresh- water 

 formation, particularly rich in fossil plants of the 

 typical Mesozoic Flora (see below, p. 56). 



The same vegetation, often abundantly rep- 

 resented, is found throughout the Jurassic for- 

 mation, which includes the Purbeck Beds, the 



